This work will investigate the role genes play in the specification of the pattern of the embryo of Drosophila melanogaster. This will involve the characterization, in particular, of the hedgehog gene locus, which is a segmental polarity class locus. This work will characterize the spatial and temporal requirements for the hedgehog gene, both embryonically and post-embryonically, by use of genetic mosaics and temperature sensitive mutations. This work also characterize the molecular architecture of the hedgehog locus and the spatial and temporal expression of RNA transcripts from this locus. In addition, this work will characterize genetically the chromosomal region around the hedgehog locus, which is known already to contain another two pattern specification loci. The understanding of how this gene and others disrupt the normal pattern of the Drosophila embryo will provide more insight into the role genes play in the embryogenesis of developing organisms, and may be applicable to an understanding of human development. This work will also provide insight into the mechanisms of gene regulation and therefore provide information valuable to understanding those disease processes, such as cancer, in which aberrant regulation of certain genes may lead to a pathological problem.